Early rearing environment impacts cerebellar growth in juvenile salmon

Abstract

SUMMARY The size and structure of an animal's brain is typically assumed to result from either natural or artificial selection pressures over generations. However, because a fish's brain grows continuously throughout life, it may be particularly responsive to the environmental conditions the fish experiences during development. Salmon are an ideal model system for studying these effects because natural habitats differ significantly from the hatchery environments in which these fish are frequently reared. For example, in the wild, salmon alevins (i.e. yolk-sac fry) are buried in the gravel, while hatchery environments lack this structural component. We show that the simple manipulation of adding stones to a standard rearing tank can dramatically alter the growth of specific brain structures in steelhead salmon alevins(Oncorhynchus mykiss). We found that alevins reared with stones grew brains with significantly larger cerebella than genetically similar fish reared in conventional tanks. This shift to a larger cerebellar size was, in turn, accompanied by changes in locomotory behaviors - behaviors that correlate strongly to the function of this brain region. We next show that hatchery fish reared in a more naturalistic setting in the wild had significantly larger brains than their lab-reared counterparts. However,relative cerebellar volumes were similar between wild-reared alevins and those reared in the complex treatment in the laboratory. Together our results indicate that, within the first three weeks of life, variation in rearing environment can result in brain differences that are commonly attributed to generations of selection. These results highlight the need to consider enrichment strategies when designing captive rearing facilities for both conservation and laboratory use.

Less is more: density influences the development of behavioural life skills in trout

“…Moreover, trout reared in barren hatchery tanks responded more rapidly to a simulated predator attack than trout from tanks containing structure. In a recent study (Kihslinger & Nevitt 2006), fish reared in hatchery tanks containing stones showed lower movement activity than fish from barren tanks. Assuming that fish in the present study respond in a similar way, low activity would explain why structured-reared fish responded to the predator attack with freezing rather than fleeing.…”

“…It is well established that spatial complexity stimulates behavioural flexibility, as well as learning and memory in mammals and birds (Young 2003). Recent studies on fish suggest similar effects, where structural enrichment in hatchery tanks have been found to improve foraging performance (Brown et al 2003), stability of social hierarchies (Galhardo et al 2008), exploratory behaviour Lee & Berejikian 2008), learning (Odling-Smee & Braithwaite 2003;Odling-Smee et al 2006), memory (Brydges et al 2008) and neural development (Kihslinger & Nevitt 2006). However, it is still unclear to what extent structural complexity can help captive reared individuals to survive in the wild (Brockmark et al 2007).…”

Environmental enrichment, sexual dimorphism, and brain size in sticklebacks

“…While some studies have supported this finding of positive effects of enrichment on brain size (DePasquale, Neuberger, Hirrlinger, & Braithwaite, 2016; Herczeg et al., 2015; Näslund, Aarestrup, Thomassen, & Johnsson, 2012), others have found either negative effects (Kotrschal, Sundström, Brelin, Devlin, & Kolm, 2012; Turschwell and White, 2016) or none at all (Burns, Saravanan, & Rodd, 2009; Kihslinger, Lema, & Nevitt, 2006). This is true not only for overall brain size, but also in the size of certain brain regions such as the cerebellum, olfactory bulb, telencephalon, and optic tectum in which both positive (Herczeg et al., 2015; Kihslinger & Nevitt, 2006; Kotrschal, Rogell, Maklakov, & Kolm, 2012; Näslund et al., 2012) and negative (optic tectum; Herczeg et al., 2015) effects of environmental enrichment have been shown. However, in the cases where positive effects have been found, the effects have been conditional to age (Näslund et al., 2012), sex, and social interactions (Herczeg et al., 2015; Kotrschal, Rogell et al., 2012) or other factors such as stress (DePasquale et al., 2016).…”

Quantitative genetic analysis of brain size variation in sticklebacks: support for the mosaic model of brain evolution

“…Strong yet indirect support for the mosaic model of brain evolution has been provided by quantitative trait locus (QTL) mapping studies [27] as well as experiments demonstrating differential plasticity in different brain regions in response to environmental conditions experienced during development (e.g. [28][29][30][31]). Nevertheless, a more direct approach to address this hypothesis would require genetic data on the magnitude and patterns of genetic covariation among the size of different brain regions.…”